The application of optical components, whether glass or plastic, in high nuclear radiation areas has always been plagued by optical component degradation from radiation induced absorption. Traditional approaches to this problem have included the uses of a heavy radiation shield and special radiation resistant glasses. These special glasses usually have inferior optical properties, such as higher transmission losses and significant changes in image hue or color for a thick optical component, due to the added chemical constituents. For a fiber optic element in a coherent bundle, it is impractical to consider the use of conventional radiation resistant glass, that is glass having cerium distributed therein, because the long glass paths in the fiber optic bundle produce a severely degraded image. It has been suggested that pure silica be used in single fiber optic elements for data communication links, because pure silica has been shown to be resistant to radiation-induced darkening, but even pure silica exhibits radiation darkening upon sufficient exposure to nuclear radiation.
A presently accepted technique to eliminate the radiation-induced absorption has been to replace the damaged optical components or to thermally anneal these components. Thermal annealing, in these applications, is usually applied for fairly long time periods in the range of between about 6 hours and 24 hours depending upon the optical component thickness, and requires that the optical component be held at temperatures at the range of between about 200.degree. C. and 300.degree. C., in order to achieve a significant absorption fading or lightening of the radiation-induced darkening. Where either complex lenses or coherent optic bundles are employed, thermal annealing of the types described is inapplicable, because the fiber optic bundles as well as the complex lenses are generally epoxy bonded, and epoxy bonding material does not withstand the elevated temperatures necessary for the thermal annealing. For this reason, it is generally not practical to attempt thermal annealing of radiation-induced absorption in either coherent fiber optic bundles or any complex lens system or fiber optic component that is fabricated with epoxy binders.
The prior art known at the present time is limited to disclosures of radiation induced darkening and changes in the refractive index due to applied radiation, and includes U.S. Pat. No. 3,364,219 issued Jan. 11, 1972 to P. Sinai; U.S. Pat. No. 3,542,536 issued Nov. 24, 1970 to R. P. Flam et al.; U.S. Pat. No. 3,173,850 issued Mar. 16, 1965 to Hood; and a digest entitled Optical Fiber Transmission II published by the Optical Society of America, 1977, which includes a paper entitled In-Situ Measurements of Growth and Decay of Radiation Damage in Fiber Optic Waveguides by E. J. Friebele and G. H. Siegal, Jr., and a paper entitled Radiation Response of Low Loss Silicone Clad Silica Fiber by George H. Siegal, Jr.